A series of small earthquakes were reported overnight in Imperial County, marking the third day of shaking in the region just east of San Diego County. A 4.1 magnitude earthquake was reported in Calipatria, which is just east of the southernmost point of the Salton Sea, at 11:53 p.m. Tuesday, according to the U.S. Geological Survey. It was preceded and followed by 2.5-magnitude earthquakes.